Ricardo Silva

Degree in Computer Science @ ISTECMSc Computation and Medical Instrumentation @ ISEP

Software Developer @ Shortcut, Lda

(blog): http://blog.ricardosilva.pt

(email): nodejs@ricardosilva.pt

Event-driven I/O server-side JavaScript environment based

on V8 Engine

JavaScript(examples)

JavaScript: Array vs ObjectInstantiation

• Arrayvar ar = []; /* ou new Array(); */

• Objectvar carColors = {}; /* ou new Object();*/

JavaScript: Array vs ObjectAdd

• Arrayvar ar = []; ar[0] = 'January';Ou ar.push(‘March’);

• Objectvar carColors = {};carColors['BMW'] = 'Red';carColors['Audi'] = 'Blue';

JavaScript: Array vs ObjectRemove

• Arrayar.splice(0,1);

• Objectdelete carColors['BMW'];

JavaScript: Array vs ObjectLookup

• Arrayvar ar = [];for (var i = 0; i < carColors.length; i++) { alert( ar[i] );};Ouvar month = ar[0];

• Objectvar carColors = {};for (var i in carColors) { alert( carColors[i] );};Ouvar colorOfBWM = carColors[‘BMW’];

JavaScript: callback Functions

var state;

function setstate (pbool, difCallBack) {if (state != pbool)

return (state = pbool), difCallBack(state);}

setstate(true, function(s){alert(s);

});

“We can keep on doing other things while waiting for the callback to be called.”

JavaScript: Events

var eventHandlers = new Object(); this.registerEvent=function(name,callback){ var eh=(eventHandlers[name])?eventHandlers[name]:(eventHandlers[name]=[]); eh[eh.length]=callback; }; this.unregisterEvent=function(name,callback){ var eh=eventHandlers[name]; if("object"==typeof eh) for(var h in eh) if(eh[h]===callback){ delete eh[h]; return; } };

JavaScript: Events

this.triggerEvent=function(name,args){ var eh=eventHandlers[name]; if("object"==typeof eh) for(var h in eh) eh[h](args); };

this.ring=function(evDelegate){ xpto.registerEvent('ring',evDelegate); };

function onRing(args){ xpto.triggerEvent('ring',args); }

Node.js

Node.js: What is?

Node.js is a platform built on Chrome's JavaScript runtime for easily building fast, scalable network applications. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient, perfect for data-intensive real-time applications that run across distributed devices.

“

”

Node.js: Companies using node!

• LinkedIn(Mobile WebApp)• Ebay(Data retrieval gateway)• GitHub(for Downloads)• Palm/HP(in WebOS)

• Yahoo!Mail• Rackspace(Cloud kick monitoring)• Voxxer(Push to Talk mobile app)

Node.js: How to install?

• $ git clone \ git://github.com/joyent/node.git• $ cd node• $ git checkout v0.6.0• $ ./configure• $ sudo make install

(windows users: download node.exe)

Node.jsDEMO

Node.js

“ Come on…, server side JS has been

around since 1996 …”

Node.js

“ …what is so special about node?

”

Node.js: Seep

Speed• Node can do ~6000 http requests / sec per CPU core• It is no problem to handle thousands of concurrent

connections which are moderately active

Node.js: V8 JS Engine

V8 JavaScript Engine• Developed by Google in Aarhus, Denmark for Google

Chrome• Translates JavaScript in Assembly Code• Crankshaft JIT (enabled in 0.6.0 by default)

Node.js: Non-Blocking I/O

Non-Blocking I/OBlocking:var fs = require('fs');var one = fs.readFileSync('one.txt','utf-8');console.log('Read file one');var two = fs.readFileSync('two.txt','utf-8');console.log('Read file two');

Non-Blocking:var fs = require('fs');fs.readFile('one.txt','utf-8',function(err,data) {

console.log('Read file one');});

fs.readFile('two.txt','utf-8',function(err,data) {console.log('Read file two');

});

DEMO

Node.js: Non-Blocking I/O

Blocking I/O

Read one.txt (20ms)

Read two.txt (10ms)

Total duration (30ms)

Node.js: Non-Blocking I/O

Non-Blocking I/O

Read one.txt (20ms)

Read two.txt (10ms)

Total duration (20ms)

Node.js: Non-Blocking I/O

Non-Blocking I/O• Close to ideal for high concurrency / high through

put, single execution stack• Forces you to write more efficient code by

parallelizing your I/O• Feels pretty much like AJAX in the browser

Node - ModulesDEMO

Websockets

Websockets: What is?

“The WebSocket specification—developed as part of the HTML5 initiative—introduced the WebSocket JavaScript interface, which defines a full-duplex single socket connection over which messages can be sent between client and server. The WebSocket standard simplifies much of the complexity around bi-directional web communication and connection management.

WebSocket represents the next evolutionary step in web communication compared to Comet and Ajax. However, each technology has its own unique capabilities. Learn how these technologies vary so you can make the right choice.”

Websockets: What is?

• Persistent connection between browser / server• The solution of the problem with RT at browser side

var ws = new WebSocket(url);ws.onopen = function() {

// When the connection opens};

ws.onmessage = function() {// When the server sends data

};

ws.onclose = function() {// When the connection is closed

};

ws.send ('Hi all!');

ws.close();

Websockets: Compatibility

Websockets: Compatibility

• We can use different transports:• HTML5 WebSockets• Flash Socket• AJAX Long Polling• Forever Iframe

Socket.io

Socket.io

“ Socket.io aims to make realtime apps possible in every browser and mobile device,

blurring the differences between the different transport mechanism. It’s care-free

realtime 100% in JavaScript.”

Socket.io: transports?

• Web Socket• Flash Socket• HTML File• XHR Polling• JSONP Polling

Socket.io: How to install?

npm install socket.io

Socket.ioDEMO

Socket.io: Other methods?

//broadcast a message to all socketssocket.broadcast.emit('event');

//no need to internally buffer this msgsocket.volatile.emit('event');

//broadcast, nut only to people in this roomsocket.broadcast.to('room').emit('event');

//broadcast to everyoneio.sockets.emit('event');io.sockets.send('hello');

Questions?

(blog): http://blog.ricardosilva.pt

(email): nodejs@ricardosilva.pt